#!/usr/bin/env python

## \file filelock.py
#  \brief python package for filelocking 
#  \author T. Lukaczyk, F. Palacios
#  \version 5.0.0 "Raven"
#
# SU2 Original Developers: Dr. Francisco D. Palacios.
#                          Dr. Thomas D. Economon.
#
# SU2 Developers: Prof. Juan J. Alonso's group at Stanford University.
#                 Prof. Piero Colonna's group at Delft University of Technology.
#                 Prof. Nicolas R. Gauger's group at Kaiserslautern University of Technology.
#                 Prof. Alberto Guardone's group at Polytechnic University of Milan.
#                 Prof. Rafael Palacios' group at Imperial College London.
#                 Prof. Edwin van der Weide's group at the University of Twente.
#                 Prof. Vincent Terrapon's group at the University of Liege.
#
# Copyright (C) 2012-2017 SU2, the open-source CFD code.
#
# SU2 is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# SU2 is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with SU2. If not, see <http://www.gnu.org/licenses/>.

import os, time, errno
from random import random

# -------------------------------------------------------------------
#  File Lock Class
# -------------------------------------------------------------------  
class filelock(object):
    """ A file locking mechanism that has context-manager support so 
        you can use it in a with statement. 
        
        Example:
        with filelock("test.txt", timeout=2, delay=0.5):
            print("Lock acquired.")
            # Do something with the locked file
            
        Inputs:
            file_name - filename to lock
            timeout   - default 10sec, maximum timeout to wait for lock
            delay     - default 0.05sec, delay between each attempt to lock
                        number incremented with a random perturbation
           
        original source: Evan Fosmark, BSD license
        http://www.evanfosmark.com/2009/01/cross-platform-file-locking-support-in-python/
    """
 
    def __init__(self, file_name, timeout=10, delay=.05):
        """ Prepare the file locker. Specify the file to lock and optionally
            the maximum timeout and the delay between each attempt to lock.
        """
        self.is_locked = False
        self.lockfile = os.path.join(os.getcwd(), "%s.lock" % file_name)
        self.file_name = file_name
        self.timeout = timeout
        self.delay = delay
 
 
    def acquire(self):
        """ Acquire the lock, if possible. If the lock is in use, it check again
            every `wait` seconds. It does this until it either gets the lock or
            exceeds `timeout` number of seconds, in which case it throws 
            an exception.
        """
        start_time = time.time()
        while True:
            try:
                self.fd = os.open(self.lockfile, os.O_CREAT|os.O_EXCL|os.O_RDWR)
                break;
            except OSError as e:
                if e.errno != errno.EEXIST:
                    raise 
                if (time.time() - start_time) >= self.timeout:
                    raise FileLockException("FileLock timeout occured for %s" % self.lockfile)
                delay = self.delay*( 1. + 0.2*random() )
                time.sleep(delay)
        self.is_locked = True
 
 
    def release(self):
        """ Get rid of the lock by deleting the lockfile. 
            When working in a `with` statement, this gets automatically 
            called at the end.
        """
        if self.is_locked:
            os.close(self.fd)
            os.unlink(self.lockfile)
            self.is_locked = False
 
 
    def __enter__(self):
        """ Activated when used in the with statement. 
            Should automatically acquire a lock to be used in the with block.
        """
        if not self.is_locked:
            self.acquire()
        return self
 
 
    def __exit__(self, type, value, traceback):
        """ Activated at the end of the with statement.
            It automatically releases the lock if it isn't locked.
        """
        if self.is_locked:
            self.release()
 
 
    def __del__(self):
        """ Make sure that the FileLock instance doesn't leave a lockfile
            lying around.
        """
        self.release()
        
class FileLockException(Exception):
    pass

#: class filelock
